Fine edged blade



0a. 20, 1931. T FR T 1,827,870

I FINE EDGED BLADE File d May 24, 19 30 Figtl 6 A uw/uzor mama Oet'.2o,193i

UNIT D S T AT E S'sPATENT orrlca THOMAS H. E5081, CAMBRIDGE, MASSACHUSETTS FINE EDGED ZBIJADE Application filed m a,

as cutting instrumentalities both from the stand-point of smooth cutting and in respect to the life of the blade. I The material I em loy in the construction We of the novel blade 0 my invention is an al- If? of steel containing a substantial amount 0 aluminum, usually combined with chromium or molybdenum or tungsten and which may be hardened by a process of nitriding, that is to say, by introducing nitrogen into, or causin it to combine with the alloy. One suitable a oy of this type is known under the name nitrallo by which it is commonly designated. en this metal is exposed to ammonia fumes under conditions of h gh temperature it becomes'nitrided upon its surface and to a slight distance below its surface and is thereby rendered extremely hard and brittle. Attempts to use this material in the so manufacture of blades heretofore have been unsuccessful partly on account of the fact that a contraction or expansion takes place in the nitriding operations whichwarps or distorts the blank. to an extent rendering sharpening difiicult or impossible. In accordance with an important feature of my invention I confine the nitriding of the blank to areas adjacent to and'including the cutting edges of the blade. This permits expansion of the portions of the blade including the cuttin edges by internal adjustment of the blank in its unnitrided areas with the result that the critical portions of the blade are preserved in a fiat condition without distortion.

In applyin my invention to a safety razor blade I provi e the blank with a central longitudinal slot substantially co-extensive in.

length with the cutting edge of the blade and effective to a certain extent in isolating the 60 body of the blade from. the portion including 1930. sci-m m. mace.

its cutting edg edged blade, lsolatmg from each other the. two portions in which the cutting edges are formed. In a blade provided with'a slot of this character the end portions which lie beyond the cutting edge of the die are unnitridedand are accor ingly soft in character so that any change in the shape of the nitrided portions may be readily absorbed without distorting the blade as a whole.

These and other features of the invention will be best understood and appreciated from the following description of a preferred embodiment thereof selected for purposes of illustration and shown in the accompanying drawings, in which- Fig. 1 is a plan view-of the blade upon an enlarged scale, showing certain end areas protected for-nitriding the process,

Fig. 2 is a similar View of the finished blade 7 I The material employedin producing blades in accordance with m invention may be any nitridable ferrous al oy having the characteristics best suited for the particular type 0 edged tool required; Nitralloy of either of the following analyses has been found satis- 1fisicicalory for the manufacture of razor Element AnalysisA ...2*2... sggassss either case the sheet nitralloy is in "suchcondition that it'may be readily blanked out. The blank thus produced is of the thickness and outline desired in the finished blade and,

e or, in thecase ofa double file as herein shown, has corner recesses defining a central'elongated portion. The blank is paste of stannic oxide 8 in water or-glycerine,

which in the subsequent nitriding bprocess is reduced to metallic tin, coating the lank and rendering it impervious to the action of'the ammonia fumes. The outline of the unnitrided area may be selected as desired but as herein shown each area is generally fanshaped and includes one end of the slot 4 and an elongated end portion of the blade.

Having prepared the blank as above outlined it is then heated in a furnace in the presence of ammonia gas at a temperature sufficiently high to insure carrying out the nitriding operation. In some cases a temperature of 930950 F. will be found suitable but I have secured entirely satisfactory results by treating the blank at a somewhat highertemperature. This results in a deeper penetration of the nitriding efi'ect and a somewhat softer resulting material than is produced at lower temperatures. The nitriding operation may be satisfactorily carried out at a temperature of 950 F. in an interval of two hours or somewhat less, while at a temperature of 1150 F. the operation may be complete in as short an interval as five minutes.

The temperature and time used for the nitriding of razor blades may be considered as determining the shaving characteristics of the finished blade. For example, a blade nitrided for two hours at 950 F. when finish sharpened in the ordinary manner gives a sharp but fairly rough'edge. If the nitriding operation be carried out at 1150 F. for twenty minutes, the penetration into, or addition of nitrogen to the exposed metal at the higher temperature being more re id and also resulting. in a softer finished prod blade when finish sharpened in the same mana sharp but smooth edge. edged blades and some prefer rou h edged blades and these different types of e ges may be procured inaccordance with my invention by variation of thenitriding temperature to suit the conditions desired.

The length of time of nitriding at any given temperature determines the depth of the nitrided case. This case must be deep enough to allow for any material which may betaken ofi duringfinish sharpening operation. The two specified temperatures and .times have been found to be satisfactory. It

is evident of course that-a compromise between a smooth and a rough edge may be oh- 7 nal edges in not, the

Some shavers prefer smooth aeaaevo as already explained, there is an appreciable internal adjustment of the alloy being treated in a blank of the form shown in Fig. 1. This may take place independently in each side portion of the blank dition and substantially nitriding process this adjustment will be absorbed in them without objectionable distortion of the blade as a whole. 7

In carrying out the nitridingprocess the two side portlons of the blade are converted into an extremely hard material having edge holding properties of a degree heretofore unattainable. The blade may be then completed by finish grinding its opposite longitudithe usual manner to form the sharpened nitrided cutting edges 12.

' Relatively soft materials such as nitralloy of the analyses given above, have a tendency to form a feather when ground to a fine edge. In the manufacture of razor blades it was found that this tendency to feather caused objectionable inequalities in the finished edge. In producing the novel blade of myinvention this objection is avoided since the finish grinding. operation is carried out upon the material hardened by the nitriding process. The material removed in grinding thereforecomes off smoothly and leaves the blade in excellent condition for honing and stropping.

. While I have. shown my invention as embodied in a safety razor blade it will be understood that it may be appliedwith advantage to fine edged tools of all descriptions and I have particularly in mind surgeons knives, pocket knives, general purposes.

7 Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is 1. A thin flexible blade of nitralloy, nitrided in an area adjacent to and including its cutting edge.

2. flexible fine edged blade of nitralloy, nitrided in an area adjacent edge and having unnitrided supporting portions.

3. A fineedged blade of nitralloy, nitrided separated bythe slot 4, and since the end areas remain in a relatively soft con- I unaffected by the to its cutting cuttingedges and cutlery for edge, and unnitrided areas mergin into the nitrided area at either end of the s t.

5. A safety razor blade comprising a thin flexible wafer of nitralloy internally apertured. and nitrided in, areas adjacent to'its cutting edge.

6. A safety razor blade comprisinga thin flexible wafer of nitralloy having a mtrided area including its cutting edge and an unnitrided area merging into the same and permitting expansion of the nitrided area without deformation of the cutting edge.

7 A safety razor blade comprismg a thin I flexible wafer of nitralloy with its opposite longitudinal edges sharpened for cutting and a central longitudinal slot, and being 'nitrided in areas coextensive withsaid slot.

8. A safety razor blade comprising a thin flexible wafer of nitralloy, the blade being nitrided and sharpened at opposite edges and having a central slot of substantially the same length as said edges and unnitrided end I areas beyond said cutting edges.

9. A safety razor blade comprising a thin flexible wafer of nitralloy with opposite cutting edges and a central internal slot, the

edge areas of the wafer being nitrided and being connected b unnitrided end portions,

whereby the nitri ing of the edge areas may be carried out without distortion of the blade as a whole. i

10. A. safety razor blade made of a nitridable alloy and comprising a flat body portion' of substantially uniform thickness and an acutely tapered cutting edge portion integral therewith, said blade being nitrided in an areaadjacent to and including its cutting edge and having an area with an unnitrided surface merging'into the same.

11. A safety razor blade made of a nitridable alloy and comprising a thin flat body portion of substantially uniformfthickness and an acutely tapered cuttin edge portion integral therewith, said blade eing nitrided in an area adjacent to and including its cutting edge. v

, Signed at Boston, Massachusetts, this 23rd day of May, 1930. v

' THOMAS H. FROST.

. mauve 

